1. Field of the Invention
The present invention relates to a new and improved fluid containment system of the type employing an inner fluid carrier conduit of one type of thermoplastic material and an outer safety conduit of different type of material maintained in spaced apart relation for containing any fluid leakage from the inner carrier. An anchor-spacer is provided to extend between the inner and outer conduits for maintaining a permanently spaced apart relation and for positively anchoring or restricting the conduits against relative longitudinal movement.
In accordance with the present invention, the inner fluid carrier conduit may be made of a relatively high grade, relatively more costly thermoplastic material of a type having a higher rating in terms of temperature, pressure and chemical resistance in contrast to an outer safety containment conduit formed of a less expensive type of thermoplastic material which is not required to have such high ratings as the inner fluid carrier conduit because normally, relatively low pressure and/or temperature conditions obtain except in the case of leaks of relatively large proportions developing in the inner carrier conduit.
2. Background of the Prior Art
In dual conduit, thermoplastic resin, containment type fluid transport systems, it is thought generally to be necessary to make both the inner fluid carrier conduit and the outer safety containment conduit out of the same type of material because of the need for similar materials when end-to-end, butt-fusion type welding is utilized in fabrication of a containment system. Heretofore, it has not been practically possible to utilize a high quality rated inner fluid carrier conduit with a less expensive outer containment conduit because of the difference in welding temperatures of different types of materials involved. For example, polyethylene resins may sell in the range of $0.58 to $0.65 a pound, but are only good for temperatures of up to 140.degree. F. whereas, polypropylene, a much more expensive resin at $2.00 or greater per pound, has a service rating of up to 210.degree. F. In terms of strength and strength to weight ratios, polypropylene may be utilized with less material being required in terms of weight for a given pressure rating and this material, even though more expensive, may be desirable from a chemical resistance standpoint when transporting different types of corrosive or deleterious chemical fluids. On the other hand, the outer containment fluid conduit is only in contact with the fluid carried when a leak develops in the inner fluid carrier conduit and thus the outer conduit is not continuously subjected to intense pressures and temperatures and does not need or require as high a quality rating as the inner fluid carrier conduit may require for a particular job installation.